The present invention relates to the treatment of wastewater, and more particularly relates to the use of alkanes to aerobically and/or anaerobically treat municipal, agricultural and industrial wastewater.
Liquid wastes are produced by most human activities including domestic sewage, agricultural processes and industrial operations. For example, according to the U.S. Department of Commerce, industrial water users discharge approximately 285 billion gallons of wastewater daily.
Some types of conventional wastewater treatment processes are microbiologically mediated. Municipal, agricultural and industrial wastewater is often treated aerobically, thereby converting pollutants into environmentally acceptable analogues. The addition of micro-bubbles of oxygen has been demonstrated to be an effective enhancement of the aerobic treatment of wastewater to lower biological oxygen demand (BOD), total dissolved solids (TDS) and total organic carbon (TOC).
Anaerobic wastewater treatment methods have also been used. For example, the addition of hydrogen has been found to enhance anaerobic processes, and to reduce unsaturated organic liquids and sludges. Anaerobic digestion is one of the oldest processes used for the stabilization of sludges. It involves the decomposition of organic matter and inorganic matter in the absence of molecular oxygen. During conventional anaerobic digestion, the organic matter in mixtures of primary settled and biological sludges is converted biologically, under anaerobic conditions, to produce methane (CH4) and carbon dioxide (CO2). During conventional anaerobic digestion, a consortium of organisms converts organic sludges and wastes. One group hydrolyzes organic polymers and lipids. A second group of anaerobic bacteria ferments the breakdown products to simple organic acids. A third group of microorganisms converts the hydrogen and acetic acid to methane gas and carbon dioxide.
Gas-liquid mixing systems are used in various processes and methods employed in the wastewater industries. Many types of mechanical devices and mixers have been developed to improve wastewater treatment by enhancing gas-liquid mixing. By enhancing gas-liquid mixing, wastewater aerobic treatment processes are improved through increased oxygen (aerobic) and hydrogen (anaerobic) dissolution and residence time.
U.S. Pat. Nos. 5,916,491 and 5,925,290, which are incorporated herein by reference, disclose apparatus and methods for mixing gas and liquid through vortex or venturi devices. The mixers are particularly suited for mixing oxygen-containing gases into industrial and municipal wastewater. Other types of gas-liquid mixers are also disclosed in U.S. Pat. Nos. 3,969,446, 4,328,175, 4,454,077, Re. 32,562, 4,645,603, 4,695,378, 4,956,080, 5,061,406, 5,073,309, 5,085,809, 5,314,076 and 5,494,576, which are incorporated herein by reference.
The bioremediation of various pollutants such as chlorinated solvents and other types of pollutants using butane-utilizing bacteria is disclosed in U.S. Pat. Nos. 5,888,396, 6,051,130, 6,110,372, 6,156,203 and 6,210,579, which are incorporated herein by reference.
In accordance with the present invention, alkanes, e.g., methane, ethane, propane and butane, can be used to effectively degrade pollutants and other materials typically found in wastewater such as chemical, industrial and municipal effluents. In a preferred embodiment, butane, having the highest solubility of the alkanes, can be used to control BOD, TOC and TDS, as well as pollutants typically found in wastewater through enhanced growth of aerobic and/or anaerobic bacteria, and possibly other microorganisms that oxidize or reduce dissolved organic matter and sludge effluents, thereby significantly decreasing the BOD of a wastestream.
Alkanes, preferably butane, may be used under aerobic and/or anaerobic conditions to enhance wastewater treatment processes during primary, secondary or tertiary treatment. Butane is highly soluble and ideally suited to serve as a microbial growth substrate, thereby significantly increasing the heterogeneous microbial community and total heterotrophic microbial population found in wastewater. This enhanced microbial population may rapidly absorb and mineralize the dissolved organic nutrients in the wastestream. To accelerate the dissolved organic nutrient reductions, the butane may be pulsed in the wastestream to create feeding frenzy/starvation cycles. After the initial growth phase, the organic matter available in the wastewater effluent may be rapidly decreased thereby reducing the BOD, TOC and TDS.
An aspect of the present invention is to provide a method of treating wastewater comprising introducing at least one alkane into the wastewater.
Another aspect of the present invention is to provide a method of treating material contained in wastewater. The method comprises stimulating growth of alkane-utilizing bacteria, and allowing the alkane-utilizing bacterial to degrade at least a portion of the material.
A further aspect of the present invention is to provide an apparatus for treating wastewater comprising means for introducing at least one alkane into the wastewater.
Another aspect of the invention is to provide an apparatus for treating wastewater comprising a wastewater containment vessel, and at least one alkane injector in flow communication with the wastewater containment vessel.
These and other aspects of the present invention will be more apparent from the following description.